Recently, organic-inorganic perovskite is attracting attention as a semiconductor material for various elements. Organic-inorganic perovskite is an ionic compound composed of an organic cation, a divalent metal ion such as Sn2+ or Pb2+, and a halogen ion. In a known three-dimensional perovskite, these ions assemble into the same crystal structure (perovskite-type structure) as perovskite (calcium titanate mineral). In a known two-dimensional perovskite, inorganic layers each made of two-dimensionally disposed inorganic frameworks, each corresponding to the octahedral portion in a perovskite-type structure, and organic layers, each made of oriented organic cations, are alternately stacked to form a layered structure. Because organic-inorganic perovskite comprises an organic structure, it can be both flexibilized and formed into a layer by solution deposition, which is advantageous in reducing the production cost of various elements. Also, because organic-inorganic perovskite has an inorganic framework and thus is expected to provide a high carrier mobility by virtue of band transport, it is extensively studied to enhance its carrier mobility.
For example, Non-Patent Literature 1 describes a field-effect hole mobility of 10−5 cm2/Vs achieved in a three-dimensional perovskite represented by CH3NH3PbI3 at room temperature. Also, Non-Patent Literature 2 describes a field-effect electron mobility of 0.1 cm2/Vs and a field-effect hole mobility of 0.01 cm2/Vs achieved in a three-dimensional perovskite of the same composition at 78 K.
On the other hand, Non-Patent Literatures 3 to 6 describe a field-effect hole mobility of 0.5 to 2.6 cm2/Vs achieved in a two-dimensional perovskite represented by (C6H5C2H4NH3)2SnI4 at room temperature.
Also, Non-Patent Literature 7 attempted to, instead of forming a two-dimensional perovskite directly on the surface of an insulator layer, to form it on an OTS (octadecyltrichlorosilane) monolayer that has been formed on the insulator layer. The same document describes a field-effect hole mobility of 0.78 cm2/Vs achieved by such a layer configuration at room temperature. Also, in Non-Patent Literature 8, an OTS monolayer was formed on the surface of an insulator layer, a part of the OTS monolayer was selectively oxygen-plasma treated to form a hydrophilic region, and a three-dimensional perovskite was formed on this hydrophilic region. The same document describes an electron mobility of 2.5 cm2/Vs at 77 K achieved in the three-dimensional perovskite thus formed.